1. Field of the Invention
The present invention relates to an ink-jet ink composition, an ink set, and an image forming method.
2. Description of the Related Art
Ink-jet recording methods use a large number of nozzles arranged in an ink-jet head, from which ink droplets are ejected when recording is performed. Ink-jet recording methods are widely used, because they make it possible to record high-quality images on a variety of recording media.
As the ink-jet recording methods, a two-part reactive ink recording method is known, in which two kinds of liquids including an ink and a treatment liquid serving to aggregate the ink are reacted so as to aggregate the ink and to promote the fixation of the ink. For example, an ink-jet recording method is disclosed, in which an ink composition containing a pigment and a resin emulsion and a reaction liquid containing a polyvalent metal salt are applied onto a recording medium. In this method, running and unevenness of images are considered to be prevented.
On the other hand, when recording is performed on plain paper or the like, sufficient performance sometimes cannot be obtained with respect to, for example, fixability (for example, scratch resistance) or resolution, in addition to color forming density. In particular, this is the case when increasing the speed of ink-jet recording, and a recording method more suitable for high speed recording using a single pass system capable of recording by one operation of a head, as opposed to a shuttle scanning system, is in demand.
In relation to the above, as an image forming method capable of high speed printing, an image recording method in which an ink composition that contains a pigment dispersed with a low molecular weight pigment dispersant and polymer particles is contacted with an acidic treatment liquid (for example, see Japanese Patent Application Laid-Open (JP-A) No. 2007-100071.) is known.
However, the image recording method described in JP-A No. 2007-100071 does not provide a sufficient ink ejection stability in some cases. The dot diameter difference between a primary color dot and a secondary color dot becomes large, whereby image quality often lowers.